Process for making flexible polyurethane foams

ABSTRACT

Process for preparing a flexible polyurethane foam by reacting a polyisocyanate and two different polyols under foam forming conditions so as to prepare a rigid foam, by crushing the rigid foam so obtained and by subjecting the flexible foam so obtained to a heat treatment. Flexible foams are obtained which do not show a major glass transition temperature between -100° C. and +25° C.

The present invention is concerned with a process to prepare flexiblepolyurethane foams.

BACKGROUND OF THE INVENTION

Conventional flexible polyurethane foams are widely known. Such foamsshow a relatively high resilience (ball rebound), a relatively lowmodulus, a relatively high sag factor and a relatively low hysteresisloss. Such foams further show a major glass-rubber transition belowambient temperature, generally in the temperature range of -100° C. to-10° C. The commonly applied relatively high molecular weight polyetherand polyester polyols in such foams are responsible for the sub-ambientglass transition temperature (Tg^(s)). These polyether and polyesterpolyols are often referred to as soft segments. Above Tg^(s) the foamdisplays its typical flexible properties until softening and/or meltingof the isocyanate-derived urethane/urea clusters ("hard domains") takesplace. This softening and/or melting temperature (Tg^(h) and/or Tm^(h))often coincides with the onset of thermal degradation of polymersegments. The Tg^(h) and/or Tm^(h) for flexible polyurethane foams isgenerally higher than 100° C., often even exceeding 200° C. At theTg^(s) a sharp decrease of the modulus of the flexible foam is observed.Between Tg^(s) and Tg^(h) /Tm^(h) the modulus remains fairly constantwith increasing temperature and at Tg^(h) /Tm^(h) again a substantialdecrease of the modulus may take place. A way of expressing the presenceof Tg^(s) is to determine the ratio of the Young's storage modulus E' at-100° C. and +25° C. as per Dynamic Mechanical Thermal Analysis (DMTAmeasured according to ISO/DIS 6721-5). For conventional flexiblepolyurethane foams the ##EQU1## is at least 25. Another feature ofTg^(s) by DMTA (ISO/DIS 6721-5) is that for conventional flexiblepolyurethane foams the maximum value of the ratio of ##EQU2## over the-100° C./+25° C. temperature range varies from 0.20-0.80 in general. TheYoung's loss modulus E" is measured by DMTA (ISO/DIS 6721-5) as well.

Conventional flexible foams are made by reacting a polyisocyanate and arelatively high molecular weight isocyanate reactive polymer, often apolyester or polyether polyol, in the presence of a blowing agent andoptionally further using limited amounts of relatively low molecularweight chain extenders and cross-linkers and optionally using additiveslike catalysts, surfactants, fire retardants, stabilisers andantioxidants. The relatively high molecular weight isocyanate reactivepolymer in general represents the highest weight fraction of the foam.Such flexible foams may be prepared according to the one-shot, thequasi- or semi-prepolymer or the prepolymer process. Such flexible foamsmay be moulded foams or slabstock foams and may be used as cushioningmaterial in furniture and automotive seating and in mattresses, ascarpet backing, as hydrophilic foam in diapers and as packaging foam.Further they may be used for acoustic applications, e.g. soundinsulation. Examples of prior art for these conventional flexible foamsare EP-10850, EP-22617, EP-111121, EP-296449, EP-309217, EP-309218,EP-392788 and EP-442631.

Conventional rigid foams are made in a similar way with the proviso thatoften the polyisocyanates have a higher isocyanate functionality, theamount of high molecular weight polyols used is lower and the amount andfunctionality of the cross-linkers is higher.

WO92/12197 discloses an energy-absorbing, open-celled, water-blown,rigid polyurethane foam obtained by reacting a polyurethanefoamformulation, comprising water which act as a blowing agent and acell-opener, in a mould wherein the cured foam has a moulded density ofabout 32 to 72 kg/m³ and a crush strength which remains constant from 10to 70% deflection at loads of less than 70 psi. The foams have minimalspring back or hysteresis.

GB2096616 discloses a directionally flexibilized, rigid, closed-cellplastic foam. The rigid foams are flexibilized in order to use them fore.g. pipe-insulation. Cells should remain closed.

U.S. Pat. No. 4,299,883 discloses a sound-absorbent material made bycompressing a foam having closed cells to such an extent that the foamrecovers to 50-66% of its original thickness. By the compression thecells are ruptured and the foam becomes flexible and resilient; it mayreplace felt. The disclosure mainly refers to polycarbodiimide foams.

EP561216 discloses the preparation of foam boards having improved heatinsulation properties, wherein the foam has anisotropic cells having alength ratio of the long and the small axis of 1.2-1.6 and a density of15-45 kg/m³ and wherein the cells have been crushed in the direction ofthe plate thickness. The disclosure actually refers to polystyreneboards.

EP641635 discloses a process for preparing foam boards, having a dynamicstiffness of at most 10 MN/n³, by crushing a board of 17-30 kg/m³density at least twice to 60-90% of its original thickness. Preferablyclosed-celled polystyrene is used. In the examples it is shown that apolystyrene foam which has been crushed showed a better heat insulationthan an uncrushed one.

U.S. Pat. No. 4,454,248 discloses a process for preparing a rigidpolyurethane foam wherein a partially cured rigid foam is softened, thencrushed and re-expanded and fully cured.

In copending patent application PCT/EP9601594 a completely new class offlexible polyurethane foams is described such foams having no majorglass-rubber transition between -100° C. and +25° C. In morequantitative terms these foams show a ratio E'₋₁₀₀° C. /E'₊₂₅° C. of 1.3to 15.0, preferably of 1.5 to 10 and most preferably of 1.5 to 7.5. Thetan.sub.δmax over the -100° C. to +25° C. temperature range is below0.2.

The apparent core density of such foams may range from 4-30 kg/m³ andpreferably ranges from 4-20 kg/m³ (measured according to ISO/DIS845).Such foams are made by crushing a rigid foam.

In said co-pending patent application it is stated that due to thecrushing the density of the foam may increase; such increase ingenerally will not exceed 30% of the density before crushing. In theexamples density increases have been reported of 18, 15 and 12.5%.

Surprisingly it has now been found that by giving these foams aheat-treatment after they have been crushed the density increase can befurther limited.

BRIEF SUMMARY OF THE INVENTION

Consequently the present invention is concerned with a process fortreating a flexible polyurethane foam having no major glass transitionbetween -100° C. and +25° C. by heating the foam to a temperaturebetween 70 and 200° C. and preferably between 90 and 80° C. for a periodof time between 0.5 minute and 8 hours and preferably 1 minute and 4hours.

The flexible foams according to the present invention also show a ratioE'₋₁₀₀° C. /E'₊₂₅° C. of 1.3 to 15.0, preferably of 1.5. to 10 and mostpreferably of 1.5 to 7.5. The tan₋₋ max over the -100° C. to +25° C.temperature range is below 0.2. The core density of such foams may rangefrom 4-30 kg/m³ and preferably ranges from 4 to 20 kg//m³ (measuredaccording to ISO 845). By the heat treatment the density increase causedby the crushing is reduced; often the density increase due to thecrushing is limited to less than 10% for foams which have been treated.

DETAILED DESCRIPTION OF THE INVENTION

In the context of the present application a flexible polyurethane foamis a crushed foam having a ball rebound (measured according to ISO 8307)of at least 40%, preferably at least 50% and most preferably 55-85% inat least one of the three dimensional directions and a sag factor (CLD65/25) of at least 2.0 (measured according to ISO 3386/1). Preferablysuch flexible foams have a Young's storage modulus at 25° C. of at most500 kPa, more preferably at most 350 kPa and most preferably between 10and 200 kPa (Young's storage modulus measured by DMTA according toISO/DIS 6721-5). Further, such flexible foams preferably have a sagfactor (CLD 65/25) of at least 3.5 and most preferably 4.5-10 (measuredaccording to ISO 3386/1). Still further such flexible foams preferablyhave a CLD hysteresis loss (ISO 3386/1) of below 55%, more preferablybelow 50% and most preferably below 45%.

In the context of the present patent application a rigid polyurethanefoam is an uncrushed foam having a ball rebound measured in thedirection of foam rise of less than 40% (ISO 8307 with the proviso thatno preflex conditioning is applied, that only one rebound value persample is measured and that test pieces are conditioned at 23° C.±2° C.and 50±5% relative humidity) and/or having a CLD 65/25 sag factormeasured in the direction of foam rise of less than 2.0 (ISO 3386/1 withthe proviso that the sag factor is determined after the firstload--unload cycle); these properties both being measured at a coredensity of the foam of 3-27 kg/m³. Preferably the ratio E'₋₁₀₀° C./E'₊₂₅° C. of such a rigid foam is 1.3-15. If in the present applicationISO 8307 and ISO 3386/1 are mentioned in relation to rigid foams theyrefer to the tests as described above including the provisos.

The flexible polyurethane foams according to the present invention areprepared by reacting a polyisocyanate and a polyfunctionalisocyanate-reactive polymer under foam forming conditions to prepare arigid polyurethane foam and by crushing this rigid polyurethane foam.

In the context of the present invention the following terms have thefollowing meaning:

1) isocyanate index or NCO index or index: the ratio of NCO-groups overisocyanate-reactive hydrogen atoms present in a formulation, given as apercentage: ##EQU3##

In other words the NCO-index expresses the percentage of isocyanateactually used in a formulation with respect to the amount of isocyanatetheoretically required for reacting with the amount ofisocyanate-reactive hydrogen used in a formulation.

It should be observed that the isocyanate index as used herein isconsidered from the point of view of the actual foaming processinvolving the isocyanate ingredient and the isocyanate-reactiveingredients. Any isocyanate groups consumed in a preliminary step toproduce modified polyisocyanates (including such isocyanate-derivativesreferred to in the art as quasi or semi-prepolymers and prepolymers) orany active hydrogens consumed in a preliminary step (e.g. reacted withisocyanate to produce modified polyols or polyamines) are not taken intoaccount in the calculation of the isocyanate index. Only the freeisocyanate groups and the free isocyanate-reactive hydrogens (includingthose of the water) present at the actual foaming stage are taken intoaccount.

2) The expression "isocyanate-reactive hydrogen atoms" as used hereinfor the purpose of calculating the isocyanate index refers to the totalof active hydrogen atoms in hydroxyl and amine groups present in thereactive compositions; this means that for the purpose of calculatingthe isocyanate index at the actual foaming process one hydroxyl group isconsidered to comprise one reactive hydrogen, one primary amine group isconsidered to comprise one reactive hydrogen and one water molecule isconsidered to comprise two active hydrogens.

3) Reaction system: a combination of components wherein thepolyisocyanates are kept in one or more containers separate from theisocyanate-reactive components.

4) The expression "polyurethane foam" as used herein refers to cellularproducts as obtained by reacting polyisocyanates withisocyanate-reactive hydrogen containing compounds, using foaming agents,and in particular includes cellular products obtained with water asreactive foaming agent (involving a reaction of water with isocyanategroups yielding urea linkages and carbon dioxide and producingpolyurea-urethane foams) and with polyols, aminoalcohols and/orpolyamines as isocyanate-reactive compounds.

5) The term "average nominal hydroxyl functionality" is used herein toindicate the number average functionality (number of hydroxyl groups permolecule) of the polyol or polyol composition on the assumption thatthis is the number average functionality (number of active hydrogenatoms per molecule) of the initiator(s) used in their preparationalthough in practice it will often be somewhat less because of someterminal unsaturation.

6) The word "average" refers to number average unless indicatedotherwise.

The foams according to the present invention are prepared by reacting apolyisocyanate (1), an isocyanate-reactive compound (2), said compound(2) having an average equivalent weight of at most 374 and an averagenumber of isocyanate-reactive hydrogen atoms of from 2 to 8, anisocyanate-reactive compound (3), said compound (3) having an averageequivalent weight of more than 374 and an average number ofisocyanate-reactive hydrogen atoms of from 2 to 6 and water to prepare arigid polyurethane foam and by crushing this rigid polyurethane foam.

Further the present invention is concerned with reaction systemscomprising the above ingredients. The present invention is alsoconcerned with a process for preparing rigid polyurethane foams usingthe above ingredients. More in particular the foams according to thepresent invention are prepared by reacting a polyisocyanate (1), apolyol (2) having a hydroxyl number of at least 150 mg KOH/g and anaverage nominal hydroxyl functionality of from 2 to 8, a polyol (3)having a hydroxyl number of from 10 to less than 150 mg KOH/g and anaverage nominal hydroxyl functionality of from 2 to 6 and water toprepare a rigid polyurethane foam and by crushing this rigidpolyurethane foam.

Suitable organic polyisocyanates for use in the process of the presentinvention include any of those known in the art for the preparation ofrigid polyurethane foams, like aliphatic, cycloaliphatic, araliphaticand, preferably, aromatic polyisocyanates, such as toluene diisocyanatein the form of its 2,4 and 2,6-isomers and mixtures thereof anddiphenylmethane diisocyanate in the form of its 2,4'-, 2,2'- and4,4'-isomers and mixtures thereof, the mixtures of diphenylmethanediisocyanates (MDI) and oligomers thereof having an isocyanatefunctionality greater than 2 known in the art as "crude" or polymericMDI (polymethylene polyphenylene polyisocyanates), the known variants ofMDI comprising urethane, allophanate, urea, biuret, carbodiimide,uretonimine and/or isocyanurate groups.

Mixtures of toluene diisocyanate and diphenylmethane diisocyanate and/orpolymethylene polyphenylene polyisocyanates may be used. Most preferablypolyisocyanates are used which have an average isocyanate functionalityof 2.1-3.0 and preferably of 2.2-2.8.

Preferably MDI, crude or polymeric MDI and/or liquid variants thereofare used said variants being obtained by introducing uretonimine and/orcarbodiimide groups into said polyisocyanates, such a carbodiimideand/or uretonimine modified polyisocyanate having an NCO value of atleast 20% by weight, and/or by reacting such a polyisocyanate with oneor more polyols having a hydroxyl functionality of 2-6 and a molecularweight of 62-500 so as to obtain a modified polyisocyanate having an NCOvalue of at least 20% by weight.

Isocyanate-reactive compounds (2) include any of those known in the artfor that purpose like polyamines, aminoalcohols and polyols. Ofparticular importance for the preparation of the rigid foams are polyolsand polyol mixtures having hydroxyl numbers of at least 150 mg KOH/g andan average nominal hydroxyl functionality of from 2 to 6. Suitablepolyols have been fully described in the prior art and include reactionproducts of alkylene oxides, for example ethylene oxide and/or propyleneoxide, with initiators containing from 2 to 8 active hydrogen atoms permolecule. Suitable initiators include: polyols, for example ethyleneglycol, diethylene glycol, propylene glycol, dipropylene glycol, butanediol, glycerol, trimethylolpropane, triethanolamine, pentaerythritol,sorbitol and sucrose; polyamines, for example ethylene diamine, tolylenediamine, diaminodiphenylmethane and polymethylene polyphenylenepolyamines; and aminoalcohols, for example ethanolamine anddiethanolamine; and mixtures of such initiators. Other suitable polyolsinclude polyesters obtained by the condensation of appropriateproportions of glycols and higher functionality polyols withpolycarboxylic acids. Still further suitable polyols include hydroxylterminated polythioethers, polyamides, polyesteramides, polycarbonates,polyacetals, polyolefins and polysiloxanes. Still further suitableisocyanate-reactive compounds include ethylene glycol, diethyleneglycol, propylene glycol, dipropylene glycol, butane diol, glycerol,trimethylolpropane, ethylene diamine, ethanolamine, diethanolamine,triethanolamine and the other initiators mentioned before. Mixtures ofsuch isocyanate-reactive compounds may be used as well.

Isocyanate-reactive compounds (3) include any of those known in the artfor that purpose, like polyamines, aminoalcohols and polyols. Ofparticular importance for the preparation of the rigid foams are polyolsand polyol mixtures having a hydroxyl value of 10 to less than 150 andpreferably of 15-60 mg KOH/g and an average nominal hydroxylfunctionality of from 2 to 6 and preferably of from 2 to 4. These highmolecular weight polyols are generally known in the art and includereaction products of alkylene oxides, for example ethylene oxide and/orpropylene oxide, with initiators containing from 2 to 6 active hydrogenatoms per molecule. Suitable initiators include: polyols, for exampleethylene glycol, diethylene glycol, propylene glycol, dipropyleneglycol, butane diol, glycerol, trimethylolpropane, triethanolamine,pentaerythritol and sorbitol; polyamines, for example ethylene diamine,tolylene diamine, diaminodiphenylmethane and polymethylene polyphenylenepolyamines; and aminoalcohols, for example ethanolamine anddiethanolamine; and mixtures of such initiators. Other suitable polyolsinclude polyesters obtained by the condensation of appropriateproportions of glycols and higher functionality polyols withpolycarboxylic acids. Still further suitable polyols include hydroxylterminated polythioethers, polyamides, polyesteramides, polycarbonates,polyacetals, polyolefins and polysiloxanes. Preferred polyols are thepolyether polyols comprising ethylene oxide and/or propylene oxide unitsand most preferably polyoxyethylene polyoxypropylene polyols having anoxyethylene content of at least 10% and preferably 10-85% by weight.Other polyols which may be used comprise dispersions or solutions ofaddition or condensation polymers in polyols of the types describedabove. Such modified polyols, often referred to as "polymer" polyolshave been fully described in the prior art and include products obtainedby the in situ polymerisation of one or more vinyl monomers, for examplestyrene and acrylonitrile, in polymeric polyols, for example polyetherpolyols, or by the in situ reaction between a polyisocyanate and anamino- or hydroxy-functional compound, such as triethanolamine, in apolymeric polyol.

The polymer modified polyols which are particularly interesting inaccordance with the invention are products obtained by in situpolymerisation of styrene and/or acrylonitrile inpoly(oxyethylene/oxypropylene) polyols and products obtained by in situreaction between a polyisocyanate and an amino or hydroxy-functionalcompound (such as triethanolamine) in a polyoxyethylene polyoxypropylenepolyol. Polyoxyalkylene polyols containing from 5 to 50% of dispersedpolymer are particularly useful. Particle sizes of the dispersed polymerof less than 50 microns are preferred. Mixtures of suchisocyanate-reactive compounds may be used as well.

The relative amount of isocyanate-reactive compound (2) and (3) orpolyol (2) and (3) may vary widely and preferably ranges from 0.1:1 to4:1 (w:w).

The relative quantities of the polyisocyanate and theisocyanate-reactive compounds to be reacted may vary within a widerange. In general an isocyanate index will be applied of from 25 to 300,preferably of from 30 to 200 and most preferably of from 40 to 150.

In order to prepare a foam water is used as a blowing agent. However ifthe amount of water is not sufficient to obtain the desired density ofthe foam any other known way to prepare polyurethane foams may beemployed additionally, like the use of reduced or variable pressure, theuse of a gas like air, N₂ and CO₂, the use of more conventional blowingagents like chlorofluorocarbons, hydrofluorocarbons, hydrocarbons andfluorocarbons, the use of other reactive blowing agents, i.e. agentswhich react with any of the ingredients in the reacting mixture and dueto this reaction liberate a gas which causes the mixture to foam and theuse of catalysts which enhance a reaction which leads to gas formationlike the use of carbodiimide-formation-enhancing catalysts such asphospholene oxides. Combinations of these ways to make foams may be usedas well. The amount of blowing agent may vary widely and primarilydepends on the desired density. Water may be used as liquid atbelow-ambient, ambient or elevated temperature and as steam.

Per 100 parts by weight of polyisocyanate (1), isocyanate-reactivecompound (2) and compound (3) or polyol (2) and polyol (3) and water,preferably the amount of compound (2) or polyol (2) ranges from 2-20parts by weight, the amount of compound (3) or polyol (3) ranges from5-35 parts by weight and the amount of water ranges from 1 to 17 partsby weight, the remainder being polyisocyanate. This encompasses anotheraspect of the invention: if a cyclic polyisocyanate and more inparticular an aromatic polyisocyanate and most in particular an MDI orpolymethylene polyphenylene polyisocyanate is used the content of cyclicand more in particular of aromatic residues in the flexible foam isrelatively high as compared to conventional flexible polyurethane foams.The foams according to the invention preferably have a content ofbenzene rings, derived from aromatic polyisocyanates, which is 30 to 56and most preferably 35 to 50% by weight based on the weight of the foam.Since polyols, polymer polyols, fire retardants, chain extenders and/orfillers which contain benzene rings may be used, the overall benzenering content of the flexible foam may be higher and preferably rangesfrom 30 to 70 and most preferably from 35 to 65% weight as measured bycalibrated Fourier Transform Infra Red Analysis.

In addition to the polyisocyanate, the isocyanate-reactive compounds andthe blowing agent, one or more auxiliaries or additives known per se forthe production of polyurethane foams may be used. Such optionalauxiliaries or additives include foam-stabilizing agents or surfactants,for example siloxane-oxyalkylene copolymers and polyoxyethylenepolyoxypropylene block copolymers, urethane/urea catalysts, for exampletin compounds such as stannous octoate or dibutyltin dilaurate and/ortertiary amines such as dimethylcyclohexylamine or triethylene diamineand/or phosphates like NaH₂ PO₄ and Na₂ HPO₄, and fire retardants, forexample halogenated alkyl phosphates such as tris chloropropylphosphate, melamine and guanidine carbonate, anti-oxidants, anti-staticagents, UV stabilisers, anti-microbial and anti-fungal compounds andfillers like latex, TPU, silicates, barium and calcium sulphates, chalk,glass fibers or beads and polyurethane waste material.

In operating the process for making rigid foams according to theinvention, the known one-shot, prepolymer or semi-prepolymer techniquesmay be used together with conventional mixing methods and the rigid foammay be produced in the form of slabstock, mouldings including foam infabric and pour-in-place applications, sprayed foam, frothed foam orlaminates with other materials such as hardboard, plasterboard,plastics, paper or metal or with other foam layers.

It is convenient in many applications to provide the components forpolyurethane production in pre-blended formulations based on each of theprimary polyisocyanate and isocyanate-reactive components. Inparticular, an isocyanate-reactive composition may be used whichcontains the auxiliaries, additives and the blowing agent in addition tothe isocyanate-reactive compounds (2) and (3) in the form of a solution,an emulsion or dispersion.

The rigid foam is prepared by allowing the aforementioned ingredients toreact and foam until the foam does not rise any more. After rise curingof the foam may be continued as long as desirable. In general a curingperiod of 1 minute to 24 hours and preferably of 5 minutes to 12 hourswill be sufficient. If desired curing may be conducted at elevatedtemperature. Subsequently the foam may be crushed. It is howeverpreferred to allow the rigid foam obtained to cool down to below 80° C.prior to crushing. The rigid foam (i.e. before crushing) preferably hasa core density of 3-27 and most preferably of 3-18 kg/m³ (ISO 845).

The rigid foam (i.e. before crushing) prepared has a substantial amountof open cells. Preferably the cells of the rigid foam are predominantlyopen.

The crushing may be conducted in any known manner and by any knownmeans. The crushing may for instance be conducted by applying mechanicalforce onto the foam by means of a flat or pre-shaped surface or byapplying variations of external pressure.

In most cases a mechanical force sufficient to decrease the dimension ofthe foam in the direction of the crushing by 1-90%, preferably by 50-90%will be appropriate. If desired crushing may be repeated and/or carriedout in different directions of the foam. Due to the crushing the ballrebound increases considerably in the direction of the crushing. Due tothe crushing the density of the foam may increase. In most cases thisincrease will not exceed 30% of the density before crushing.

Although it is difficult to give more precise directions for thecrushing since it will inter alia depend on the density of the foam, therigidity of the foam, the type of crushing device used, we believe thoseskilled in the art are sufficiently aware of the phenomenon of crushingof polyurethane foams that they will be able to determine theappropriate crushing manner and means with the above guidance, certainlyin the light of the following examples.

By crushing the ball rebound is increased at least in the direction ofcrushing. The increase is at least 10%.

After crushing the flexible foam is subjected to the heat treatmentdescribed before. This treatment may be conducted in any way known inthe art; e.g. by passing hot air having the desired temperature over thefoam for the desired time period; by placing the foam in a furnace,which is set at the desired temperature, for the desired period of time;by moving the foam through such a furnace so that the residence time ofthe foam in said furnace reflects the desired time period or by usinginfra-red or microwave heating.

After the beat-treatment a novel flexible foam is obtained which hasexceptional properties. Despite the fact that the foam is flexible, itdoes not show a significant change of the Young's storage modulus E'over a temperature range from -100° C. to +25° C., as described before.The oxygen index of the foam prepared from aromatic polyisocyanatespreferably is above 20 (ASTM 2863). Further it shows a Young's storagemodulus at 25° C. of at most 500 kPa, preferably at most 350 kPa, mostpreferably between 10-200 kPa and a sag factor (CLD 65/25, ISO 3386/1)of at least 2.0, preferably at least 3.5 and most preferably of 4.5-10.CLD hysteresis loss values for the foams are below 55% and preferablybelow 50% (which is calculated by the formula ##EQU4## wherein A and Bstand for the area under the stress/strain curve of the loading (A) andunloading (B) as measured according to ISO 3386/1). Still further thesefoams can be manufactured with a very low or even negative Poisson'sratio as determined by lateral extension studies under compression ofthe foams. Finally compression set values of the foams are generallylow, preferably below 40% (ISO 1856 Method A, normal procedure).

If the Tg^(h) is not too high the foam might be used in thermoformingprocesses to prepare shaped articles. Preferably the Tg^(h) of the foamis between 80° C. and 180° C., most preferably between 80° C. and 160°C. for such thermoforming applications. Further it was found that foams,which have been made by using a relatively low amount of the polyolshaving a low molecular weight, show a small or non-visible Tg^(h) (themodulus change at Tg^(h) is small or the modulus changes gradually untilthe foam thermally decomposes) by DMTA; such foams however may be usedfor thermoforming activities as well.

Further the foams show good load-bearing properties like compressionhardness values without the use of external fillers together with a goodresilience, tear strength and durability (fatigue resistance) even atvery low densities. In conventional flexible foams often high amounts offiller need to be used to obtain satisfactory load-bearing properties.Such high amounts of fillers hamper the processing due to a viscosityincrease.

The foams of the present invention may be used as cushioning material infurniture and automotive and aircraft seating and in mattresses, ascarpet backing, as hydrophilic foam in diapers, as packaging foam, asfoams for sound insulation in automotive applications and for vibrationisolation in general. The foam according to the present inventionfurther may be used together with other, conventional flexible foams toform composites, like e.g. in mouldings; such composites may also bemade by allowing the ingredients for making the conventional flexiblefoam to form said foam in a mould in the presence of the foam accordingto the present invention or alternatively by allowing the ingredientsfor making the rigid foam according to the present invention to formsaid rigid foam in a mould in the presence of the conventional flexiblefoam followed by crushing the moulding so obtained. Further the foamsaccording to the present invention may be used as textile cover, ascover for other type of sheets, as carpet underlay or felt-replacement;the so-called flame lamination technique may be applied to adhere thefoam to the textile, the carpet or the other sheet. In this respect itis important to note that the foam according to the present invention issuitable to be cut in sheets of limited thickness, e.g. of about 1 cmand less. Still further the foam according to the present invention maybe used as insulation material around pipes and containers.

The invention is illustrated by the following examples.

EXAMPLE

A rigid polyurethane foam was made by feeding three components to themixing head of a Komet high pressure, multiple stream dispensingmachine, pouring the mixture so obtained into an open wooden box(100×50×50 cm) and allowing the mixture so obtained to react and foam;the applied index was 102. The first component contained 20 parts byweight (pbw) of a polyoxyethylene polyoxypropylene polyol havingdiethylene glycol as initiator, a nominal hydroxyl functionality of 2,an oxyethylene content (except the initiator) of 20.2% by weight (alltipped) and a hydroxyl value of 30 mg KOH/g; 0.75 pbw of DABCO™ T9, astannous octoate catalyst from Air Products and 0.56 pbw of Irganox™5057, an antioxidant from Ciba Geigy. The second component contained7.55 pbw of polyethyleneglycol having a molecular weight of 200, 2.35pbw of triethylene glycol, 4 pbw of water and 0.06 pbw of NaH₂ PO₄. Thethird component was a mixture of 56.6 pbw of polymeric MDI having an NCOvalue of 30.7% by weight and an isocyanate functionality of 2.7 and 43.4pbw of a uretonimine modified MDI having an NCO value of 31% by weight,an isocyanate functionality of 2.09, a uretonimine content of 17% byweight and 2,4'-MDI content of 20% by weight. The total amount of thethree components was 3 kg.

The rigid foam so obtained had a core density (ISO 845) of 13.1 kg/m³and a ball rebound (ISO8307) of 27% measured in the direction of foamrise.

Four samples were cut (10×10×5.5 cm) out of the core of this foam andcrushed in the foam rise direction at 23° C., 45° C., 70° C. and 100° C.respectively by using an INSTRON 1122 testing machine with flat plateshaving an surface area slightly larger than the contact surface area(10×10 cm) of the foam. Prior to testing the samples were preconditionedfor 24 hours at 23° C. and at a relative humidity of 50-55% and then thefoam was kept for 10 minutes at the selected crushing temperature beforecrushing. The crushing procedure involves at first one crush at 100mm/min up to 70% CLD, followed by 20 respective load/unload cycles up to70% CLD at 500 mm/min, all in the direction of foam rise. Subsequent tothe crushing the foams were allowed to recover freely for two hours atthe crushing temperature. Hereafter the foams were stored prior tofurther testing for 24 hours, at 23° C. and a relative humidity of50-55%. The crushed samples had a core density (ISO 845) of 17.0, 16.5,16.1 and 17.7 kg/m³ respectively and a ball rebound (ISO8307) of 60, 57,57 and 59% respectively measured in the direction of crushing.

These four crushed samples were placed in a furnace at 100° C. for 2hours. After the samples were cooled to ambient temperature the coredensities (ISO 845) were 13.6, 13.5, 13.6 and 14.3 kg/m³ respectively.Similar recovery was obtained when the foam was heated to 80° C. for 7hours, to 140° C. for 3 minutes or to 160° C. for 1 minute.

I claim:
 1. Process for treating a flexible polyurethane foam having aE'₋₁₀₀° C. /E'₊₂₅° C. ratio of 1.3-15 wherein the foam is heated to atemperature of between 70° C. and 200° C. for a period of time between0.5 minute and 8 hours.
 2. Process for reducing the density of a crushedfoam comprising treating a crushed flexible foam having an E'₋₁₀₀° C./E'₊₂₅° C. ratio of 1.3-15 wherein the foam is heated to a temperatureof between 70° C. and 200° C. for a period of time between 0.5 minuteand 8 hours.
 3. Process according to claim 2, the foam having aresilience of at least 50%.
 4. Process according to claim 3, the foamhaving a resilience of 55-85%.
 5. Process according to claim 2, the foamhaving a core density of 4-30 kg/m³.
 6. Process according to claim 5,the foam having a core density of 4-20 kg/m³.
 7. Process according toclaim 2, the foam having a content of benzene rings of 30 to 70% byweight based on the weight of the foam.
 8. Process according to claim 7,the foam having a content of benzene rings of 35 to 65% by weight basedon the weight of the foam.
 9. Process according to claim 2, the foamhaving E'₋₁₀₀° C. /E'₊₂₅° C. ratio of 1.5-10.
 10. Process according toclaim 2, the foam having a sag factor (CLD 65/25) of at least 3.5. 11.Process according to claim 10, the foam having a sag factor (CLD 65/25)of 4.5-10.
 12. Process according to claim 2, the foam having a Young'sstorage modulus at 25° C. of at most 500 kPa.
 13. Process according toclaim 12, the foam having a Young's storage modulus at 25° C. of 10-200kPa.
 14. Process according to claim 2, wherein the foam is heated to atemperature between 90° C. and 180° C. for a period of time between 1minute and 4 hours.
 15. Process according to claim 2 wherein theflexible foam has a ball rebound of at least 40% in at least one of thethree dimensional directions.
 16. Process according to claim 15 whereinthe flexible foam has a ball rebound of at least 55-85% in at least oneof the three dimensional directions.